This invention relates to a separator device for separating a gas/solids mixture rising through a vertical riser tube. It relates more particularly to a fenestrated centrifugal terminator for use in an internally circulating fluid bed reactor.
It has long been recognized that inefficient separation of spent catalyst from the reaction products in a fluidized catalytic cracking unit can lead to after-cracking, with a detrimental impact on the yield structure. Various forms of simple gas/catalyst separation devices were conceived and implemented over the years and these were typically a type of ballistic separator using a tee arrangement at the top of the reactor. An example of such tee arrangement can be seen in Milne et al, U.S. Pat. No. 5,370,789, issued Dec. 6, 1994. Another major concern with internally circulating fluidized bed reactors is the increase in thermal cracking as the riser temperature is raised in search of better product selection. In this instance, not only must the catalyst be rapidly separated from the product vapor, but the vapour residence time must be reduced rapidly to avoid excessive thermal degradation.
A recent separator design that attempts to address the above problems is a new riser terminator developed by Stone and Webster. That terminator is described in an article by Michael A. Silverman entitled "New Stone & Webster FCC Riser Terminator" published in the Circulating Fluidized Bed-4 (CFB4) Conference Preprints, Somerset U.S.A. (1993) pp 479-483. This new terminator was able to decrease the residence time from riser outlet to cyclone outlet from 24.4 to 5.5 seconds. It also showed a residence time of 0.7 seconds from the riser outlet to inertial separator vapor outlet.
Because of the very high riser velocities and mass fluxes that are used in commercial riser reactors or internally circulating fluid bed reactors, an even faster separation of solids and gases would be desirable. It is also important that exceedingly short separation times be accomplished with very high separation efficiencies.
It is the object of the present invention to provide a centrifugal terminator with residence times as low as 20 milliseconds or lower, combined with a solids separation efficiency of 99.5% or greater.